This invention relates to a cryosurgical probe. It relates more particularly to a relatively low cost, self-contained probe particularly suited for operations involving the eye.
In probes of this general type, fluid is circulated through the probe tip to maintain the tip at a very low temperature, e.g., -30.degree. C. When the probe tip is brought into contact with human tissue, the tissue at the point of contact becomes frozen and adheres to the tip. Thus if the probe is withdrawn, the adhered tissue is pulled away with it. Thus in a cataract removal operation, for example, the patient's eye lens becomes adhered to the probe and is extracted.
There are in use today various self-contained probes which carry their own refrigerant supply. Basically these units consist of a housing containing a reservoir of a suitable refrigerant such as Freon gas maintained as a liquid under high pressure. When it is desired to use the probe, the reservoir is opened allowing the refrigerant therein to flow to the probe tip where the refrigerant evaporates and, in the process, cools itself and the tip.
A particularly desirable disposable probe of this type is disclosed in U.S. Pat. No. 3,910,278. That probe is able to operate consistently for a relatively long period of time, e.g. 3 to 5 minutes on a moderately sized supply of refrigerant, e.g. 3 gm. This is because it maintains two phase flow of refrigerant to the probe tip. That is, the refrigerant flows through a capillary tube to the probe tip as a saturated vapor and liquid so that cooling at the tip is caused primarily by evaporation of the refrigerant right at the working end of the tip.
As described in detail in that patent, this two-phase flow is achieved by isolating and insulating the refrigerant flowing through the capillary tube from the cold gas exhausting from the probe tip thereby inhibiting regenerative cooling of the incoming refrigerant. Preferably this is accomplished by bathing the capillary tube through which refrigerant flows to the probe tip in room temperature liquid refrigerant. Since the specific volume of the fluid flowing to the tip is kept relatively high in this manner, the tip can be maintained at its -30.degree. C working temperature for as long as 3 to 5 minutes, which is quite long enough for a cataract removal or removal of foreign material from the vitreous humor.
With probes of this type, it is desirable to be able to warm the probe tip following completion of surgical procedure in order to facilitate separating the tip from the tissue to which it is adhered. One probe of which we are aware (described in U.S. Pat. No. 3,524,446 ) accomplishes this by flooding the probe tip with liquid refrigerant maintained at room temperature. However, that probe requires several separate valves to enable the probe to operate properly in both its freeze and defrost modes. Furthermore, that probe must carry a relatively large supply of refrigerant, e.g. 10 to 12cc in order to adequately cool the tip for the required time during the freeze mode and yet have sufficient refrigerant left to warm the tip during the defrost mode. Accordingly the probe itself is rather large and unwieldy.
These prior disposable probes having a defrost capability are also disadvantaged because they are relatively complex and difficult to make due to the valving required. Consequently, they are relatively expensive considering that they are intended to be throw-away items.